Objectives are: (1) Develop an inexpensive, rapid-response, high-sensitivity and selective electrochemical sensor for oxides of nitrogen (NO{sub x}) for compression-ignition, direct-injection (CIDI) OBD II systems; (2) Explore and characterize novel, effective sensing methodologies based on impedance measurements and designs and manufacturing methods that are compatible with mass fabrication; and (3) Collaborate with industry in order to (ultimately) transfer the technology to a supplier for commercialization. Approach used is: (1) Use an ionic (O{sup 2-}) conducting ceramic as a solid electrolyte and metal or metal-oxide electrodes; (2) Correlate NO{sub x} concentration with changes in cell impedance; (3) Evaluate sensing mechanisms and aging effects on long-term performance using electrochemical techniques; and (4) Collaborate with Ford Research Center to optimize sensor performance and perform dynamometer and on-vehicle testing. Work in FY2011 focused on using an algorithm developed in FY2010 in a simplified strategy to demonstrate how data from controlled laboratory evaluation could be applied to data from real-world engine testing. The performance of a Au wire prototype sensor was evaluated in the laboratory with controlled gas compositions and in dynamometer testing with diesel exhaust. The laboratory evaluation indicated a nonlinear dependence of the NO{sub x} and O{sub 2} sensitivity with concentration. For both …